.\"
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.\" Common Development and Distribution License ("CDDL"), version 1.0.
.\" You may only use this file in accordance with the terms of version
.\" 1.0 of the CDDL.
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.\" source.  A copy of the CDDL is also available via the Internet at
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.\" Copyright 2016 Joyent, Inc.
.\"
.Dd June 02, 2016
.Dt MC_GETCAPAB 9E
.Os
.Sh NAME
.Nm mc_getcapab
.Nd get device capabilities
.Sh SYNOPSIS
.In sys/mac_provider.h
.Ft boolean_t
.Fo prefix_m_getcapab
.Fa "void *driver"
.Fa "mac_capab_t capab"
.Fa "void *cap_data"
.Fc
.Sh INTERFACE LEVEL
illumos DDI specific
.Sh PARAMETERS
.Bl -tag -width Fa
.It Fa driver
A pointer to the driver's private data that was passed in via the
.Sy m_pdata
member of the
.Xr mac_register 9S
structure to the
.Xr mac_register 9F
function.
.It Fa capab
A value which indicates the capability being asked about.
For a full list of capabilities, see the
.Sx CAPABILITIES
section of
.Xr mac 9E .
.It Fa cap_data
Capability specific data that may need to be filled in.
The type of data used is listed in the
.Sx CAPABILITIES
section of
.Xr mac 9E .
.El
.Sh DESCRIPTION
The
.Fn mc_getcapab
entry point is called to determine whether or not a device supports a
specific capability.
The capability in question is specified in
.Fa capab
and the list of possible capabilities is listed in the
.Sx CAPABILITIES
section of
.Xr mac 9E .
.Pp
Capabilities are generally only queried once for a given device.
An instance of a device cannot change whether or not it supports a given
capability after it has been queried by the system.
.Pp
Each capability has its own specific kind of data that a device driver
needs to fill in as part of declaring that it supports a given capability.
That data is present in
.Fa cap_data .
The device driver should cast
.Fa cap_data
to the appropriate structure and fill it in.
The structures to use for a given capability are all listed in the
.Sx CAPABILITIES
section of
.Xr mac 9E .
.Pp
The return value is used to indicate whether or not a device driver
supports the given capability.
If it does, then the device driver should return
.Sy B_TRUE
after filling in
.Fa cap_data .
Otherwise, whenever it encounters an unsupported or unknown capability,
it should return
.Sy B_FALSE .
Many device drivers employ
.Sy switch
statements and return
.Sy B_FALSE
from their default case statement.
The system will present unknown capabilities to device drivers and they must
properly return
.Sy B_FALSE .
.Pp
The driver has access to its soft state by casting the
.Fa driver
argument to the specific structure.
The device driver is responsible for any necessary locking.
.Pp
Many capabilities are related to features of hardware.
However, all hardware and firmware has the possibility of having bugs.
It is recommended that any capability that is supported have some form of
tunable, whether in the form of a
.Sy MAC_PROP_PRIVATE
driver-specific property and/or a
.Xr driver.conf 5
property to disable it.
This way when problems are discovered in the field, they can be worked around
without requiring initial changes to the device driver.
.Sh CONTEXT
This function is generally only called from
.Sy kernel
context.
.Sh RETURN VALUES
If the device driver supports the specified capability
.Fa capab ,
then it should return
.Sy B_TRUE .
Otherwise, it should return
.Sy B_FALSE .
.Sh EXAMPLES
The following example shows how a driver might structure its
.Fn mc_getcapab
entry point.
.Bd -literal
#include <sys/types.h>
#include <sys/mac_provider.h>

/*
 * Note, this example merely shows the structure of the function. For
 * the purpose of this example, we assume that we have a device which
 * has members that indicate whether the various capabilities have been
 * enabled and that they are read-only after the driver has had its
 * mc_start(9E) entry point called.
 */

#define	EXAMPLE_LSO_MAX		65535

static boolean_t
example_m_getcapab(void *arg, mac_capab_t cap, void *cap_data)
{
	example_t *ep = arg;

	switch (cap) {
	case MAC_CAPAB_HCKSUM: {
		uint32_t *txflags = cap_data;

		/*
		 * The actual flags used here should be replaced with
		 * what the device actually supports. If the device
		 * doesn't support checksums, then this case statement
		 * shouldn't exist.
		 */
		*txflags = 0;
		if (ep->ep_tx_hcksum_enable == B_TRUE)
			*txflags = HCKSUM_IPHDRCKSUM;
		break;
	}

	case MAC_CAPAB_LSO: {
		mac_capab_lso_t *lso = cap_data;

		if (ep->ep_lso_enable == B_TRUE) {
			lso->lso_flags = LSO_TX_BASIC_TCP_IPV4;
			lso->lso_basic_tcp_ipv4.lso_max = EXAMPLE_LSO_MAX;
		} else {
			return (B_FALSE);
		}
		break;
	}

	default:
		return (B_FALSE);
	}

	return (B_TRUE);
}
.Ed
.Sh SEE ALSO
.Xr mac 9E ,
.Xr mac_register 9F ,
.Xr mac_register 9S
